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I couldn't find any docs explaining the contents of /sys/block/<dev>/stat, so I wrote up the following. I'm not completely sure it's accurate - Jens, could you give a yea or nay on this? In particular, the counts of read/write IOs and read/write sectors are incremented in different places - it looks like they both increment as the request is being finished, but I'm not completely sure of that. Cc: Jens Axboe <axboe@suse.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
83 lines
3.2 KiB
Plaintext
83 lines
3.2 KiB
Plaintext
Block layer statistics in /sys/block/<dev>/stat
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===============================================
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This file documents the contents of the /sys/block/<dev>/stat file.
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The stat file provides several statistics about the state of block
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device <dev>.
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Q. Why are there multiple statistics in a single file? Doesn't sysfs
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normally contain a single value per file?
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A. By having a single file, the kernel can guarantee that the statistics
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represent a consistent snapshot of the state of the device. If the
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statistics were exported as multiple files containing one statistic
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each, it would be impossible to guarantee that a set of readings
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represent a single point in time.
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The stat file consists of a single line of text containing 11 decimal
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values separated by whitespace. The fields are summarized in the
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following table, and described in more detail below.
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Name units description
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---- ----- -----------
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read I/Os requests number of read I/Os processed
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read merges requests number of read I/Os merged with in-queue I/O
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read sectors sectors number of sectors read
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read ticks milliseconds total wait time for read requests
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write I/Os requests number of write I/Os processed
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write merges requests number of write I/Os merged with in-queue I/O
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write sectors sectors number of sectors written
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write ticks milliseconds total wait time for write requests
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in_flight requests number of I/Os currently in flight
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io_ticks milliseconds total time this block device has been active
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time_in_queue milliseconds total wait time for all requests
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read I/Os, write I/Os
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=====================
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These values increment when an I/O request completes.
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read merges, write merges
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=========================
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These values increment when an I/O request is merged with an
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already-queued I/O request.
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read sectors, write sectors
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===========================
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These values count the number of sectors read from or written to this
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block device. The "sectors" in question are the standard UNIX 512-byte
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sectors, not any device- or filesystem-specific block size. The
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counters are incremented when the I/O completes.
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read ticks, write ticks
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=======================
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These values count the number of milliseconds that I/O requests have
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waited on this block device. If there are multiple I/O requests waiting,
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these values will increase at a rate greater than 1000/second; for
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example, if 60 read requests wait for an average of 30 ms, the read_ticks
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field will increase by 60*30 = 1800.
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in_flight
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=========
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This value counts the number of I/O requests that have been issued to
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the device driver but have not yet completed. It does not include I/O
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requests that are in the queue but not yet issued to the device driver.
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io_ticks
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========
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This value counts the number of milliseconds during which the device has
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had I/O requests queued.
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time_in_queue
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=============
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This value counts the number of milliseconds that I/O requests have waited
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on this block device. If there are multiple I/O requests waiting, this
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value will increase as the product of the number of milliseconds times the
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number of requests waiting (see "read ticks" above for an example).
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